Dougie McDonald hands over an object thrown on to the pitch in Celtic's win at Dundee United. His assistant has now quit refereeing. Photograph: Lynne Cameron/PA

The Scottish Football Association fears further resignations from referees and officials after Steven Craven, the assistant referee who overturned a penalty award to Celtic during their game at Dundee United nine days ago, quit today.

The level of abuse Craven has received for that intervention has led him to end his refereeing career, the SFA admitted tonight. "I can confirm that I have met with the relevant match officials and members of the referee departments regarding the events that occurred during the recent match between Dundee United and Celtic," said Stewart Regan, the SFA's chief executive. "I can also confirm that Steven Craven has tendered his resignation and will no longer officiate in the professional game. I hope to conclude the investigation within the next 48 hours and will make further comment at that time."

The SFA believes Craven may not be the last to adopt that stance, with worries growing within Hampden Park over continually negative scrutiny of referees. Kenny Clark, a former top-flight official in Scotland, has claimed that his ex-colleagues have been "receiving letters with razor blades in them and having their windows smashed" by irate fans.

Celtic have made their displeasure with decisions plain recently. The referee for Sunday's Old Firm derby, Willie Collum, was castigated by the club's manager Neil Lennon for awarding a dubious penalty to Rangers. The SFA has thus far not publicly backed Collum over his performance.